THE CHROMATIN IN THE LIVING ARBACIA PUNCTULATA EGG, AND THE CYTOPLASM OF THE CENTRIFUGED EGG AS PHOTOGRAPHED BY ULTRA-VIOLET LIGHT

¹ The Marine Biological Laboratory, Woods Hole; the Biological Laboratory, Princeton University; and the Rockefeller Institute for Medical Research, New York City

1. Photographs of living immature, mature and dividing eggs of Arbacia punctulata, taken with ultra-violet light of wave length 2537 A°, show an absorption, indicating presence of nucleic acid compounds, in the nucleolus, chromatin network and chromosomes. The photographs with ultra-violet light are similar to those of sections of fixed material stained with Heidenhain's haematoxylin taken with visible light. The chromatin network and chromosomes cannot be seen with visible light in the living egg.

2. In the centrifuged egg, with ultra-violet light, the clear layer shows greatest absorption, indicating the localization of nucleic acid compounds in this layer. With visible light, this layer appears dark and granular in sections stained with Heidenhain's haematoxylin, much as it does with ultra-violet light. It is optically empty in the living centrifuged egg with visible light. This layer represents the matrix or ground substance of the normal uncentrifuged egg. The matrix of the nucleus and the layers of granules (mitochondria, yolk, pigment and oil) are relatively non-absorbent with ultra-violet light.